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What is Curly Dock Poisoning?

Curly Dock (of the Smartweed (Polygonaceae) family) is an herbaceous perennial, which is a plant that lives more than two years, and grows continuously from the same root. Curly dock is nonnative to the United States, but grows in all regions of the United States and Canada. Listed as an invasive weed in over 15 states, it infiltrates 16 crops including pastures, hay crops, small grains, orchards and lawns. A health risk to many types of livestock, curly dock is known to accumulate oxalates and nitrates in its leaves and stems. If consumed in great quantity, the animal can experience potentially fatal oxalate poisoning.

Seeds and vegetation are toxic to poultry and cause gastrointestinal distress in cattle, among other animals. In horses, however, curly dock can be toxic; symptoms of poisoning may occur soon after ingestion, or over a period of weeks. Thankfully, not all instances have fatal outcomes. Curly Dock, a rhubarb relative, is also known as sour or yellow dock.  Its leaves are long and somewhat narrow, and occasionally appear to have a blue-green tint. The “curly” part of the plant’s name is ascribed to the crisped, rolled-up edges of the leaves, which are said to have the look of “crispy bacon.” Flowers are small, green and three-winged, and turn brown when mature. Seedlings that appear in the fall typically flower in May, and continue to bloom through summer into October.

The plant is readily found in cultivated fields, ditches, pastures, and along roadsides across the United States. It is a hardy, deep-rooted plant that grows in stalks ranging from two to four feet.  The plant reproduces and spreads when large numbers of its lightweight seeds are carried by wind and water across great distances.  A single plant can produce more than 40,000 seeds.  When used by humans as an herbal preparation or as food, Curly Dock’s tart, lemony flavor is appreciated and enjoyed. The stalks of the plants are used in salads, and the root is said to have medicinal uses; the plant is often cited for its anti-inflammatory properties and is also used for dental care.  

Because Curly Dock is so deep-rooted, it is very difficult to control with usual means. In small patches, the plants can be hand-pulled. In larger areas, summertime mowing is only effective if done on a continual basis across a few growing seasons. Herbicides can be effective, but only if applied in multiple treatments, and systemically. Chemical treatment is most effective when applied in the fall, and allowed to develop and grow within the plant until it reaches the roots.

Pastures should be walked daily in search of new vegetation or nitrate accumulating weeds. Being able to identify the stalks and leaves of all plants in your horse’s living environment may save the lives of your equine companions. Staying vigilant to grass clippings blown from nearby fields and pastures is another important part of pasture management.

Curly Dock (Rumex crispus) is an herbaceous perennial that grows in all regions of the United States and Canada; the invasive weed is poisonous to many types of livestock, but poses the most significant risk to the lives of horses.

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Symptoms of Curly Dock Poisoning in Horses

  • Loss of appetite
  • Depression
  • Unwillingness to stand (recumbency)
  • Difficulty breathing
  • Bluish-colored mucous membranes
  • Lack of coordination
  • Slobbering
  • Staggering
  • Muscle tremors
  • Weakness
  • Convulsion
  • Erratic behavior
  • Abortion
  • Coma
  • Sudden death

Causes of Curly Dock Poisoning in Horses

The primary reason for the low number of fatalities is that the pungent taste of these plants does not, under normal conditions, appeal to livestock. If healthy forage or nutritious feed is abundantly available, horses do not typically turn to plants such as curly dock as a source of nutrition. In times of drought or when grass becomes parched or short, and hay has not yet been provided, poisonous plants may be approached by horses as sources of food, despite the acrid taste. Due to its potential to accumulate oxalates, all parts of the curly dock, including its leaves, stems and seeds, are toxic. While many cases of Curly Dock poisoning do not have fatal outcomes, horses typically become very ill after ingesting the plant.

When ingested in small amounts, or when mixed with other, healthy vegetation, most horses will show symptoms of gastrointestinal disturbances. In cases of more significant ingestion, the horse may show extreme toxicity symptoms within a few hours. A subtle tremor may lead to convulsions, which will signify some type of neurological impact. At worst, horses may become weak, collapse or experience sudden death.

Diagnosis of Curly Dock Poisoning in Horses

If poisoning is suspected, a veterinarian should be called immediately. Diagnosis will rely heavily on the owner’s report of the incident, plants in the environment, exposure to any toxins, changes in behavior and symptoms of illness. First, the veterinarian will want to eliminate any other cause of toxicity and confirm presence of the plant in the environment. In the case of death, diagnosis will depend on an autopsy. The only method to determine the presence of toxicity is through testing. 

Treatment of Curly Dock Poisoning in Horses

Any poisoned horse will need immediate veterinary care and hospitalization may be required. If possible, the vet will try to empty the stomach of the horse to flush the poison. In some cases, activated charcoal is effective because it works to absorb any ingested poison. Laxatives may be administered to speed up elimination of the poison. In addition, supportive care specific to the symptoms may be offered such as oxygen or intravenous fluids; fluid therapy can help to stimulate organ function.

Recovery of Curly Dock Poisoning in Horses

The best approach is prevention. Sadly, many horses have succumbed to plant poisoning due to improper pasture and nutritional management. Horses will not eat toxic weeds if provided with adequate hay and pasture. Learn to recognize plants and weeds, and install a program to eradicate growth. Make sure to examine any hay or feed for infiltrations of weeds.